Numerous brushes of this type have been disclosed, e.g., in DE 31 48996.
One problem in the construction of such brushes can be seen in the fact that the unit consisting of the brush and the collector generates noise during the operation. This noise is caused by the contact surface of the brush sliding along the surface of the collector such that the lamellar structure of the collector surface induces vibrations that cause airborne sound that are perceived as noise. Numerous proposals pertaining to the reduction of this noise have been disclosed. In all new proposals, it must be observed that the contact resistance between the brush and the collector cannot be excessively small. In addition, the brush should have a sufficient resistance to abrasion, i.e., the brush cannot be excessively soft.
According to one proposal, the contact surface is inclined relative to the axis of the collector or the outer surface of the collector. In this case, the contact surface is correspondingly beveled. However, this results in a sharp-edged transition between the contact surface and the lower lateral edge of the brush, i.e., the brush merely adjoins the collector with one edge during the initial phase of operation.
In brushes of this type, the hard surface produced during the pressing of the graphite mixture is usually not removed and the attainable noise reduction is quite low. If the surface skin of the brush is removed after the pressing, it is possible that the edge will break.
It is also known to provide the contact surface of the brush with longitudinal grooves over the entire surface. These grooves extend in the transverse direction, i.e., in the circumferential direction of the collector. However, this measure results in an insignificant reduction in the noise level.
According to the invention, it is proposed to incline the contact surface relative to the axial direction of the collector, and to provide the contact surface with one or more grooves that extend in the transverse direction within the lower region, with said grooves being machined into the surface while the hard surface skin is simultaneously removed.
It was established that two or three grooves are sufficient, with the lowest groove being open toward the bottom. The contact surface is curved in accordance with the cylindrical surface of the collector. The incline of the contact surface relative to the outer surface of the collector lies on the order of 6-10 degrees, preferably at approximately 8 degrees. The ideal incline depends on the fact that electric currents should be transmitted by the brush, as well as other factors.
For example, ideal inclination decreases proportionally with the intensity of the electric currents to be transmitted.